This invention relates to a method for manufacturing a part by metal injection molding of metal powder mixed with a binder, by which method individual components of the part are produced as separately molded green compact sections and then as debindered brown compact sections which are joined together to form a two or more part multi-part brown compact and sintered in the assembled state. The method is for example suitable for manufacturing thermally stressed engine parts of geometrically complex structure.
It is known to manufacture parts of high geometrical complexity from different metals, for example special steels, case-hardened and tempered steels, intermetallic phases, light metals on titanium basis and the like, by metal injection molding (MIM), with complete use of the material and with little or no reworking. In metal injection molding, a metal powder is initially mixed with a binder made of thermoplastics and waxes to form a feedstock which is free-flowing and processable in an injection molding process. The binder is then removed from the part, or green compact, created by injection molding by the use of solvents or heat, so that a porous molded part—called the brown compact—is available and has the same dimensions as the green compact. In a subsequent heating process, the brown compact is sintered at slightly below the melting temperature of the respective metal in a sintering furnace, usually in an inert gas atmosphere or sometimes also in a vacuum. After sintering, in which the brown compact shrinks to the required final dimensions, the final molding is obtained. Reworking is generally not necessary.
It is known from DE 103 31 397 A1 to manufacture parts of geometrically complicated shape for an aircraft gas turbine, in this case individual stator vane ring segments each having two or more stator vanes plus an inner shroud section and an outer shroud section, by metal injection molding. With this method, the inner and outer shroud sections are each prefabricated separately as a brown compact and then pre-sintered without shrinkage. The pre-sintered vane and shroud brown compacts are then joined together to form a stator vane segment and fixed relative to one another in the assembled position by clamps, and then sintered. A close contact at the mating surfaces, which is required for making a firm connection between the individual parts, is not assured by the arrangement of clamps. Also, the restricted freedom of movement due to fixing by means of clamps can result in unwelcome deformations and cracks in the assembled stator vane segment during sintering.
US 2007/0202000 A1 describes a method for connecting two components manufactured by metal injection molding, where the two components to be connected have differing shrinkage during sintering. The two components have projections or recesses, respectively, which positively engage in one another. During sintering, the component enclosing the projections of the other component exerts a pressure on these projections. The following connection of the two components is assured primarily by the projections.